Bioprosthetic valves have been developed that attempt to mimic the function and performance of a native valve. Flexible leaflets are fabricated from biological tissue such as bovine pericardium. In some valve designs the biological tissue is sewn onto a relatively rigid frame that supports the leaflets and provides dimensional stability when implanted. Although bioprosthetic valves can provide excellent hemodynamic and biomechanical performance in the short term, they are prone to calcification and cusp tears, among other failure modes, requiring reoperation and replacement.
Attempts have been made to use synthetic materials, such as polyurethane, among others, as a substitute for the biological tissue, to provide a more durable flexible leaflet prosthetic valve, herein referred to as a synthetic leaflet valve (SLV). However, synthetic leaflet valves have not become a valid valve replacement option since they suffer premature failure, due to, among other things, suboptimal design and lack of a durable synthetic material.
The leaflets move under the influence of fluid pressure. In operation, the leaflets open when the upstream fluid pressure exceeds the downstream fluid pressure and close when the downstream fluid pressure exceeds the upstream fluid pressure. The free edges of the leaflets coapt under the influence of downstream fluid pressure closing the valve to prevent downstream blood from flowing retrograde through the valve.
It has been found that in some very flexible leaflet prosthetic valves, the leaflets do not open and close in a controlled manner. The durability of the leaflets is largely controlled by the character of bending exhibited by the leaflet during the opening-closing cycle. Small radius bends, creases and particularly intersecting creases, can produce high stress zones in the leaflet. These high stress zones can cause the formation of holes and tears under repetitive loading. If the leaflet bending is unrestricted, not only do creases form, but crease intersections lead to formation of large three dimensional structures (e.g., surface disruptions) that oppose bending and slow down the leaflet motion, both in opening and closing. This slow down of leaflet motion leads to an increase in closing volume; that is, the volume of blood that travels back through the valve during the closing phase in order to close the valve. It is advantageous to minimize closing volume.
Further, the flexible nature of the very flexible leaflet can create regions of blood pooling behind the leaflet when in the open position potentially causing blood clots to form at the leaflet base and near the attachment of the leaflet to the frame.
What is needed in the art is a flexible leaflet prosthetic valve that provides a more controlled leaflet movement that reduces closing volume and potential for blood pooling behind the leaflet and near any attachment of the leaflet to a support structure.